The present invention relates to an electromagnetic drive device in which a magnet rotor formed of a permanent magnet is rotatably accommodated in a coil frame with a coil wound around on an outer periphery thereof so that the magnet rotor rotates when a direct current is supplied to the coil, and a light quantity adjustment device for adjusting a light quantity of an optical image pick-up device through a torque generated in the magnet rotor.
Generally, as disclosed in Japanese Utility Model No. 2541274, in an optical device such as a camera, an opening/closing blade member is provided at an image pick-up lens part on an optical axis of image light so that the blade member shields light under a so-called shutter control or adjusts the quantity of light under a so-called exposure control. Such a blade member is connected to a magnet rotor through a transmission member, and arranged to open and close when a current is supplied to a coil wound around the magnet rotor. In such an electromagnetic drive device comprising the magnet rotor and the coil, the magnet rotor is rotatably supported in a coil frame having a hollow tubular shape and formed of a resin and the like, and the coil is wound around an outer periphery of the coil frame. A yoke (magnetic induction member) covers an outer surface of the coil frame.
Conventionally, such a coil frame has a structure divided laterally (up and down) or vertically (left and right) with respect to a rotational shaft of the magnet rotor. The magnet rotor is disposed inside the coil frame, and the coil is wound around the outer periphery thereof, thereby integrally assembling the device. When the coil frame is divided laterally, it is necessary to provide a taper for easy molding. Also, it is sometimes difficult to smoothly rotate the magnet rotor due to a positional misalignment between upper and lower bearing portions when the magnet rotor is supported inside the coil frame, thereby causing a problem in manufacture.
The present invention relates to an improved structure of the coil frame divided vertically, thereby reducing a size of the device. Conventionally, a tubular (cylindrical) coil frame is divided vertically at the center thereof into two portions, and a magnet with a rotational shaft is disposed inside the coil frame. A transmission member protruding outwardly from the coil frame is attached to a rotational shaft of the magnet rotor. The coil is wound on concave grooves individually formed in each of the two divided coil frame halves, respectively. The two coil frame halves are joined at a center portion from which the rotational shaft of the magnet rotor protrudes, and are integrated with an adhesive tape.
In the structure of the conventional electromagnetic device, the coil frame halves with the coil wound around thereon are joined at the center portion where the rotational shaft is located, so that the tubular coil frame has a large diameter in a radial direction. When the coil has, for example, 200 turns, it is necessary to provide a winding margin such as the concave groove in each of the coil frame halves for winding 100 turns. Further, it is necessary to provide bearing portions for supporting the shaft at the center of the coil frame and thick wall portions for forming the bearing portions, thereby increasing a size of the device in the radial direction.
As disclosed in Japanese Utility Model No. 2606159, in an optical image pick-up device such as a video camera and still camera, a shutter blade for shielding light or a stop blade for adjusting light is disposed in a lens-barrel provided with an image pick-up lens to control a quantity of light. The blade member is disposed on an image pick-up optical axis in the lens-barrel to be rotatable or slidable, and an electromagnetic drive device drives and controls the blade member. In such an electromagnetic drive device, a magnet rotor is rotatably accommodated inside a coil frame with a conductive coil wound around an outer periphery thereof. A rotation of the magnet rotor is transmitted to the blade member for opening and closing or adjusting a photographing optical axis to increase and decrease an aperture diameter. Such a structure has been widely used in which the magnet rotor is polarized in two poles N and S, and a magnetic field is generated in the coil to rotate the rotor when a direct current is supplied to the coil.
In the electromagnetic drive device, the magnet rotor is rotatably supported in the coil frame having a hollow tubular shape and formed of a resin and the like, and a torque is transmitted to the blade member from the rotational shaft through a transmission arm. Accordingly, the coil frame has a structure divided into two portions for accommodating the magnet rotor inside. After the rotor is disposed inside the coil frame, the two portions are joined and the coil is wound around an outer periphery of the coil frame. The coil frame is divided vertically into two portions along the rotational shaft of the magnet rotor or divided laterally into two portions in a direction perpendicular the rotational shaft.
When the coil frame is divided vertically, even if a diameter of the coil frame is reduced to make the device small, since the two coil frame halves are joined (connected) vertically in a longitudinal direction, it is possible to join the two halves with little misalignment, thereby making it easy to install the magnet rotor. However, when the coil frame is divided vertically along the rotational shaft of the magnet rotor, it is necessary to provide bearing portions. Conventionally, as disclosed in Japanese Utility Model No. 2606159, a bearing concave portion is formed in each of the coil frame halves, and the coil frame halves are joined to support the rotational shaft.
When the bearing concave portion is formed in each of the coil frame halves and the coil frame halves are joined to support the rotational shaft of the magnet rotor, it is difficult to smoothly rotate the magnet rotor if the concave portions have low dimensional accuracy so that a positional misalignment occurs when the coil frame halves are joined. Recently, the device has been made small, and it is necessary to accurately form a bearing portion to support a rotational shaft of a rotor having a diameter of only about 1 mm. In view of electric power consumption, it is necessary to provide a bearing portion of a rotational shaft with a low mechanical loss such as friction.
In view of the problems described above, the present invention has been made, and an object of the present invention is to provide an electromagnetic drive device with a compact size and easy to manufacture, and a light quantity adjustment device using the same, wherein a coil is wound around a coil frame divided vertically into two portions along a rotational shaft of a rotor without dividing the coil, and it is possible to prevent a breakage of the coil wire by a groove at a joint line of the coil frame.
Another object of the present invention is to provide an electromagnetic drive device in which it is easy to form a coil frame for supporting a magnet rotor with a small mechanical loss at a bearing portion of a rotational shaft, thereby rotating the magnet rotor smoothly.
Further objects and advantages of the invention will be apparent from the following description of the invention.